In order to bring the working surface, i.e. the outer surface of a roll and especially a rolling mill roll to the precise predetermined contour which the mill must have in its finished state to be able to properly roll metal strip or other workpieces, it is known to subject the roll to an electroerosion process. This process can be referred to as EDT (electric discharge texturing) and enables the profile or contour of the surface of the roll to be imparted to it with a high degree of precision.
In the EDT process, spark erosion of the surface of the roll results in a removal of material which leaves the surface of the roll with a predetermined uniform surface roughness with a mean roughness value Ra and a certain number of peaks per unit area. In this process one or more electrodes are brought into juxtaposition with the surface of the roll over a precisely controlled gap, a dielectric liquid such as kerosine or oil can flood this gap and in this position of the electrode vis-a-vis the surface of the roll, an electrical generator applies a high frequency machining pulse which locally causes a discharge through the dielectric, the formation of a crater, the removal of a particle from the surface and a uniform distribution of such microcratering over the surface. The pulse forms, in the presence of the conductive particles in the dielectric, a dipole bridge across which the pulse current begins to flow. That heats a locally trough-shaped volume of the material at the surface of the roll above its melting point, causing that heated portion to expand. In the discharge channels which are formed, a gas bubble is created and when the erosion pulse terminates causes collapse of that discharge channel, the molten volume is drawn away from the surface of the roll. That leaves a trough-shaped cavity which is reproduced in a micropattern over the entire surface and enables the roll to be shaped with high precision and to very narrow tolerances.
In the rolling process the roll serves as a tool for deforming and texturing the rolled product. The roll is applied to the rolled product with the rolling force to cause the deformation of the rolled product. However, under the rolling force in the mill stand, the rolling conditions have tended in the past to change especially in the first few meters of the rolling operation after a new roll has been installed as a result of the fact that peaks on the surface of the roll tend to break off at the high specific forces which develop between the roll and the workpiece. The result is nonuniform wear of the roll, the presence of impurities on the product surface and abrasion against the product surface. The impurities are undesirable in further deformation and coating processes. The roll may require premature remachining and excessive waste of material from the roll.
As a consequence, it has been the practice to follow the electroerosion of the roll by a process for treating the roll surface to improve the quality thereof for rolling. Generally the roll is removed from the EDT texturing machine and treated with brushes and/or by means of a chemical treatment or etching so that the peaks are preferentially treated. The peaks of the roughness structure are thereby broken. To that end the roll is usually placed in a separate brushing machine or in a chemical path for etching. This increases the cost of fabricating and handling the roll. It is especially disadvantageous that in the brush treatment, there are no defined processing conditions so that the process is hardly reproducible. The process is not amenable to automation and as a consequence, the entire finishing operation in roll manufacture is detrimentally affected.